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Using antitranspirants to control leaf moisture loss

Antitranspirants are products that, when applied to foliage, reduce the rate of foliar transpiration. Comprised of a wax, plastic, or resin, the application of an antitranspirant leaves a thin, protective film atop the leaf surface (Brent-Jones, 1966; Watson & Himelick, 1997; Watson & Himelick, 2013). The film may last for several weeks, though re-application is necessary if there is a desire to reduce transpiration rates for elongated periods of time. Furthermore, if leaves are still growing then the film will crack and its efficacy will be reduced as a result (Watson & Himelick, 2013), meaning application prior to the leaves being fully-grown is perhaps not wholly effective. In addition to this, as the spray dries to become invisible, there are no means to ascertaining how much has been applied or retained upon the leaf at any given time, and nor is there a way in which the extent of cracking can be ascertained (Brent-Jones, 1966).

When used improperly (applying too much and potentially also at overly-frequent intervals), application of an antitranspirant may be detrimental to plant health. Reductions in root and shoot growth may be observed, in such instances (Lee & Kozlowski, 1974; Watson & Himelick, 1997). However, when used properly, their application can increase growth rate and aid with plant establishment via the retention of more water (Davenport et al., 1972; Steinberg et al., 1990). There is also distinct variability in the efficacy of different products, though not only do the products themselves differ but differing environmental conditions, as well as different species, result in varying levels of efficacy across product ranges and also within the same product (Hipps & Nicoll, 1997; Watson & Himelick, 2013). For instance, on species including the pines (Pinus spp.), application can significantly reduce transpiration (by bolstering the already waxy leaf surface), though can also reduce the rate of photosynthesis very markedly; mainly due to reduced CO2 diffusion (Davenport et al., 1974; del Amor et al., 2010; Kozlowski & Davies, 1975; Watson & Himelick). When applied to some species, certain antitranspirants are also toxic.

Because application of an antitranspirant reduces transpiration, leaf surfaces may also potentially warm up considerably more during warmer periods. This can damage the leaf tissues, and result in dysfunction through injury (Watson & Himelick, 2013), leading to early senescence of leaves that have become damaged (Neumann, 1974). Root and shoot growth may therefore be impacted negatively, in response (Ranney et al., 1989; Wellburn et al., 1974).

Such products are nonetheless useful for regulating water loss post-transplanting (Berkowitz & Rabin, 1988), and may be particularly effective during the spring months (Harris & Bassuk, 1995). However, the reliance on such products should not replace good transplanting practice (Watson & Himelick, 1997), and care should be used when applying any type of antitranspirant. It is preferable to apply an antitranspirant only lightly, for an overall net benefit in response to an application (Watson & Himelick, 2013).

Granted, it should be noted however that once water availability within the soil reaches the lowest critical threshold, even the application of an antitranspirant is of no aid (Steinberg et al., 1990). It may therefore be wise to combine such application, in times of significant drought, with irrigation.